Voided latex particles containing functionalized outer shells

ABSTRACT

The wet adhesion of a coating composition may be improved through the use of voided latex particles as opacifying agents which contain a hollow interior as well as an outer shell of a polymer containing functional groups such as amino, 1,3-diketo, urea or ureido. Other types of functional groups may be introduced to the outer shell polymer in order to vary other desired characteristics of the coating. The voided latex particles are non-film-forming.

TECHNICAL FIELD

The present application relates to latex particles and emulsionpolymerization processes for producing such particles. In particular,the present application relates to aqueous emulsion polymerizationprocesses for preparing “hollow” or “voided” latex particles and thelatex particles prepared therefrom, which are useful as non-film-formingopacifiers.

BACKGROUND OF THE INVENTION

Paints and coatings play an important role in preserving, protecting andbeautifying the objects to which they are applied. Architectural paintsare used to decorate and extend the service life of the interior andexterior surfaces of residential and commercial buildings.

“Hollow latexes (i.e., voided latex particles) which arenon-film-forming have been developed for use as opacifiers in paints andother coatings. As such, they are typically used as full or partialreplacements for other opacifying agents such as titanium dioxide.Performance properties impacted include, but are not limited to, wetadhesion, block resistance, scrub resistance, solvent resistance andstain resistance. “Wet adhesion” refers to the level of adhesion to asubstrate surface that a coating exhibits under conditions of highhumidity, condensation, or precipitation. “Blocking” is said to occurwhen two painted surfaces adhere to each other when pressed together.“Scrub resistance” is a measure of the resistance of the paint toabrasive wear. “Solvent resistance” is a measure of the resistance ofthe paint to deterioration due to exposure to various organic solvents.“Stain resistance” refers to the ease with which contaminants such aslipstick, crayon, ketchup and mustard can be removed from a paintedsurface. Limiting the negative impact on the performance properties ofcoatings containing voided latex particles thus would be desirable.

SUMMARY OF THE INVENTION

The present invention provides a voided latex particle comprising ahollow interior (void) and an outer shell, wherein the outer shell iscomprised of an outer shell polymer having a glass transitiontemperature (Tg) of at least above 45° C., or of least 50° C., or ofleast 60° C., and bearing functional groups. The functional groups may,for example, be selected from 1,3-diketo, amino, ureido, urea, hydroxyl,silane, phosphate, polyether, epoxy, fluorocarbon, aldehyde, ketone,acetoacetyl functional groups or combinations thereof. Such particlesare non-film-forming opacifying agents which can be added to coatingcompositions such as paints, not only to enhance hiding but also toimpart improved wet adhesion and/or block resistance and/or othercharacteristics.

The invention also provides a process for forming non-film-formingvoided latex particles, wherein the process comprises contactingmulti-stage emulsion polymer particles comprising a core and an outershell with a swelling agent, wherein:

the core comprises a hydrophilic component such as a polymer of at leastone hydrophilic monoethylenically unsaturated monomer;

the outer shell comprises an outer shell polymer having a Tg of at leastabove 45° C., or at least 50° C., or at least 60° C., and bearingfunctional groups selected from 1,3-diketo, amino, ureido, urea,hydroxyl, silane, phosphate, polyether, epoxy, fluorocarbon, aldehyde,ketone, acetoacetyl, or combinations thereof; and

the swelling agent is capable of swelling the core.

The invention additionally furnishes multi-stage emulsion polymerparticles useful for forming non-film-forming voided latex particles,wherein a multi-stage emulsion polymer particle comprises a core and anouter shell. The core comprises a hydrophilic component (e.g., a polymerof at least one hydrophilic monoethylenically unsaturated monomer) andis capable of being swollen with a swelling agent. The outer shellcomprises an outer shell polymer having a Tg of at least above 45° C.,or at least 50° C., or at least 60° C., and bearing functional groupsselected from 1,3-diketo, amino, ureido, hydroxyl, silane, phosphate,polyether, epoxy, fluorocarbon, aldehyde, ketone, acetoacetyl, orcombinations thereof.

DESCRIPTION OF FIGURES

FIG. 1 illustrates in schematic form an exemplary process which can beused to obtain multi-stage emulsion polymer particles and voided latexparticles in accordance with the invention.

FIG. 2 illustrates the impact of acrylic latex modification, voidedlatex particle opacifier level, and functionalized monomer content ofthe outer shells of the voided latex particles on wet adhesion to agloss alkyd substrate, as explained in more detail in the Examples.

DETAILED DESCRIPTION OF THE INVENTION

The voided latex particles of the present invention may be characterizedas being “non-film-forming.” By “non-film-forming” it is meant that thevoided latex particles will not form a film at ambient temperature orbelow, or in other words will only form a film at temperatures aboveambient temperature. For the purposes of this specification, ambienttemperature is taken as being in the range of 15° C. to 45° C. Thus, forexample, when incorporated into an aqueous coating composition, appliedto a substrate temperature and dried or cured at ambient temperature orbelow, the voided latex particles do not form a film. The voided latexparticles generally remain as discrete particles in the dried or curedcoating. The voided latex particles are capable of functioning asopacifiers; that is, when added in sufficient amount to a coatingcomposition that would otherwise be transparent when dried, they renderthe dried coating composition opaque. By the term “opaque”, it is meantthat the refractive index of a coating composition has a higherrefractive index when the voided latex particles of the presentinvention are present in a coating composition as compared to the samecoating composition not including the voided latex particles of thepresent invention wherein the refractive index is measured after thecoatings are dry to the touch. The term “outer shell polymer” refers tothe outer layer of the particle of the present invention after swelling.

The voided latex particles of the invention generally comprise a hollowinterior and an outer shell which encloses the hollow interior, althoughas will be explained subsequently in more detail one or more additionallayers may be present between the outer shell and the interior void ofeach particle. Generally speaking, the voided latex particles may have adiameter of at least 200 nm, at least 250 nm, at least 300 nm, at least350 nm, or at least 400 nm and a diameter of not more than 1200 nm, notmore than 700 nm, not more than 650 nm, not more than 600 nm, not morethan 550 nm, or not more than 500 nm. The hollow interior generally hasa diameter of at least 100 nm, at least 150 nm, or at least 200 nm, buttypically is not more than 600 nm or not more than 500 nm or not morethan 400 nm in diameter. The thickness of the layers surrounding thehollow interior, including the outer shell and also any additionallayers which may be present, generally is from 30 to 120 nm. Typically,the voided latex particles will be approximately spherical in shape,although oblong, oval, teardrop or other shapes are also possible.

The outer shell is polymeric and may, for example, be comprised of athermoplastic polymer. The outer shell polymer has a glass transitiontemperature (Tg) above ambient temperature, typically at least above 45°C., at least 50° C., at least 60° C., at least 70° C., at least 80° C.or at least about 90° C. The Tg of the outer shell polymer may be, forexample, from 60° C. to 140° C. Although the outer shell polymer may bea homopolymer, more typically it will be a copolymer comprised ofrecurring polymerized units of two or more different monomers,especially ethylenically unsaturated monomers such as those capable ofbeing polymerized by free radical polymerization. The outer shellpolymer is further characterized by bearing one or more different typesof functional groups, particularly reactive, polar, chelating and/orheteroatom-containing functional groups. These functional groups may bevaried and chosen as desired to modify certain characteristics of thevoided latex particles, such as the wet adhesion, scrub resistance(washability), stain resistance, solvent resistance and block resistanceproperties of a coating composition which includes the voided latexparticles. For example, the functional groups may be selected from1,3-diketo, amino, ureido and urea functional groups and combinationsthereof. Suitable 1,3-diketo functional groups include acetoacetatefunctional groups, which may correspond to the general structure—OC(═O)CH₂C(═O)CH₃. Suitable amino functional groups include primary,secondary and tertiary amine groups. The amino functional group may bepresent in the form of a heterocyclic ring. The amino functional groupmay, for example, be an oxazoline ring. Other types of functional groupsuseful in the present invention include, for example, hydroxyl (—OH),silane (e.g., trialkoxysilyl, —Si(OH)₃), phosphate (e.g., PO₃H and saltsthereof), fluorocarbon (e.g., perfluoroalkyl such as trifluoromethyl),polyether (e.g., polyoxyethylene, polyoxypropylene), and epoxy (e.g.,glycidyl). In one embodiment, the functional group contains a Lewis basesuch as the nitrogen atom of an amine. In another embodiment, thefunctional group contains a hydroxyl functional group. The functionalgroup may be reactive; for example, the functional group may be capableof reacting as an electrophile or a nucleophile. The functional group,or a combination of functional groups in proximity to each other, may becapable of complexation or chelation.

The functional groups may be introduced into the outer shell polymer bydifferent means. In one embodiment, the functional groups are introducedinto the outer shell polymer during formation of the polymer, forexample by polymerization of one or more polymerizable monomers bearingthe desired functional groups (hereinafter “functionalized monomer”).Such polymerization may be carried out as a copolymerization wherein oneor more functionalized monomers are copolymerized with one or morenon-functionalized monomers. The monomers having functional groupsdescribed herein may be added at any stage in the preparation of themulti-stage emulsion provided that polymers bearing such functionalgroups at least partially or completely reside in the outer shellpolymer of the particles after swelling.

For example, the outer shell polymer may be a copolymer of a vinylaromatic monomer (e.g., styrene) and a free radical polymerizableethylenically unsaturated monomer containing a functional group such asa 1,3-diketo, amino, ureido, urea, hydroxyl, silane, fluorocarbon,aldehyde, ketone, phosphate or polyether functional group. The copolymermay contain one or more other additional types of comonomers, such asalkyl (meth)acrylates (e.g., methyl methacrylate). The proportions ofdifferent monomers may be varied as may be desired to impart certaincharacteristics to the resulting outer shell polymer. Typically, thecopolymer contains from 0.1 to 10 weight % of free radical polymerizableethylenically unsaturated monomer(s) containing the functional group(s).Such a copolymer may further comprise 80-99.9 weight % of a vinylaromatic monomer such as styrene and 0-10 weight % (e.g., 0.1-10 weight%) of an alkyl (meth)acrylate such as methyl methacrylate.

The free radical polymerizable ethylenically unsaturated monomer maycontain a (meth)acrylate (i.e., acrylate or methacrylate) group or a(meth)acrylamide (i.e., acrylamide or methacrylamide) group. Such(meth)acrylate and (meth)acrylamide groups are capable of participatingin free radical copolymerization with the vinyl aromatic monomer.Allylic groups may also be used to provide a polymerizable site ofunsaturation.

Imidazolidinone (meth)acrylic monomers such as2-(2-oxo-1-imidazolidinyl)ethyl (meth)acrylates andN-(2-(2-oxo-1-imidazolidinyl)ethyl (meth)acrylamides may be utilized ascomonomers, for example. Other suitable free radical polymerizableethylenically unsaturated monomers containing functional groups usefulin the practice of the present invention include, without limitation,acetoacetoxy(meth)acrylates (e.g., acetoacetoxyethyl methacrylate,AAEM), allyl acetoacetate, methylolated diacetone (meth)acrylamides,aminoalkyl(meth)acrylates (including dialkyl and monoalkylaminoethyl(meth)acrylates), and ethylenically unsaturated polymerizableaziridinyl monomers (such as those described, for example, in U.S. Pat.No. 3,719,646, incorporated herein by reference in its entirety for allpurposes). Other suitable free radical polymerizable ethylenicallyunsaturated monomers containing useful functional groups includehydroethylethylene urea methacrylate (HEEUMA) and aminoethylethyleneurea methacrylate (AEEUMA). The free radical polymerizable ethylenicallyunsaturated monomer may contain a plurality of functional groups on eachmonomer molecule; for example, the monomer may bear two or more ureaand/or ureido groups per molecule, such as the compounds described inU.S. Pat. No. 6,166,220 (incorporated herein by reference in itsentirety for all purposes). Illustrative examples of particular freeradical polymerizable ethylenically unsaturated monomers suitable foruse in the present invention as functionalized monomers include, but arenot limited to, aminoethyl acrylate and methacrylate,dimethylaminopropylacrylate and methacrylate,3-dimethylamino-2,2-dimethylpropyl-1-acrylate and methacrylate,2-N-morpholinoethyl acrylate and methacrylate, 2-N-piperidinoethylacrylate and methacrylate, N-(3-dimethylaminopropyl)acrylamide andmethacrylamide, N-(3-dimethylamino-2,2-dimethylpropyl)acrylamide andmethacrylamide, N-dimethylaminomethyl acrylamide and methacrylamide,N-(4-morpholino-methyl)acrylamide and methacrylamide, vinylimidazole,vinylpyrrolidone, N-(2-methacryloyloxyethyl)ethylene urea,N-(2-methacryloxyacetamidoethyl)-N, allylalkyl ethylene urea,N-methacrylamidomethyl urea, N-methacryloyl urea, 2-(1-imidazolyl)ethylmethacrylate, 2-(1-imidazolidin-2-on)ethylmethacrylate,N-(methacrylamido)ethyl urea, glycidyl (meth)acrylates,hydroxyalkyl(meth)acrylates such as 2-hydroxyethyl(meth)acrylates,gamma-(meth)acryloxypropyltrialkoxysilanes,N,N-dimethyl(meth)acrylamides, diacetone(meth)acrylamides, ethyleneglycol (meth)acrylate phosphates, polyethylene glycol (meth)acrylates,polyethylene glycol methyl ether (meth)acrylates, diethylene glycol(meth)acrylates and combinations thereof.

In another embodiment of the invention, a precursor polymer is firstprepared and then reacted so as to introduce the desired functionalgroups and thus provide the outer shell polymer. For example, aminefunctional groups may be introduced to the outer shell polymer byreacting a precursor polymer bearing carboxylic acid groups with anaziridine. In this example, the precursor polymer may be a polymerprepared by polymerizing an ethylenically unsaturated carboxylic acidsuch as (meth)acrylic acid, optionally together with other monomers suchas alkyl (meth)acrylates and/or vinyl aromatic monomers (e.g., styrene).

The voided latex particles of the present invention may be prepared bydifferent methods, including, for example, by processes which utilizemulti-stage emulsion polymer particles. The multi-stage emulsion polymerparticles may comprise a core comprising a polymer of at least onehydrophilic monoethylenically unsaturated monomer and an outer shellcomprising an outer shell polymer bearing functional groups selectedfrom 1,3-diketo, amino, ureido, urea, hydroxyl, epoxy, silane,polyether, fluorocarbon, aldehyde, ketone, acetoacetyl, or phosphatefunctional groups or combinations thereof. The multi-stage emulsionpolymer particles may be contacted with a swelling agent, such as abase, which is capable of swelling the core, particularly in thepresence of water.

The swollen core causes the outer shell to expand, such that when thepolymer particles are subsequently dried and/or re-acidified the outershell remains enlarged in volume and a void is created within theparticle as a result of the shrinkage of the swollen core. As theswollen core shrinks, it may form a coating on the interior surface ofthe shell of the particle. The voided latex particles may each contain asingle void. However, in other embodiments of the invention, theindividual voided latex particles may contain a plurality of voids(e.g., a voided latex particle may contain two or more voids within theparticle). The voids may be connected to each other through pores orother passageways. The voids may be substantially spherical in shape,but may adopt other forms such as void channels, interpenetratingnetworks of void and polymer, or sponge-like structures.

The aforementioned multi-stage emulsion polymer particles may beprepared by sequential emulsion polymerization, using a batch processwhere the product of one stage is used in the stage that follows. Forinstance, the product of the core stage may be used to prepare theproduct of the next stage, be it an outer shell or an intermediateencapsulating polymer stage. Similarly, the shell stage is prepared fromthe product of the core stage or, when there are one or moreencapsulating polymer stages, an intermediate encapsulating polymerstage.

The core component of the multi-stage emulsion polymer particles isgenerally located at or near the center of such particles. However, inone embodiment, the core may coat and surround a seed which is comprisedof a polymer different from the polymer used to prepare the core. Inthis embodiment, for example, the seed may comprise a polymer which isnon-hydrophilic in character; i.e., the seed polymer may be ahomopolymer or copolymer of one or more non-ionic monoethylenicallyunsaturated monomers such as methyl methacrylate. In one embodiment, theseed polymer is a methyl methacrylate homopolymer which is resistant toswelling by the swelling agent used to swell the core. The seedtypically has a particle size of from about 30 to about 200 nm or fromabout 50 to about 100 nm. To form the core, the seed may be coated withanother polymer which is comprised of at least one hydrophilicmonoethylenically unsaturated monomer, optionally in combination with atleast one non-hydrophilic monoethylenically unsaturated monomer such asan alkyl (meth)acrylate and/or a vinyl aromatic monomer. Sufficienthydrophilic monoethylenically unsaturated monomer should be used,however, such that the resulting polymer is capable of being swollenwith a swelling agent such as an aqueous base. In one embodiment, forexample, the polymer used to coat the seed and provide the corecomponent is a copolymer of methyl methacrylate and methacrylic acid,the methacrylic acid content of the copolymer being about 30 to about 60weight percent.

The core comprises a hydrophilic component that provides a sufficientdegree of swelling for hollow or void formation. In some embodiments,the hydrophilic component is provided in the form of a hydrophilicmonomer used to prepare the core polymer (i.e., a polymer used to obtainthe core includes polymerized units of a hydrophilic monomer, in anamount effective to render the core polymer hydrophilic). In otherembodiments, the hydrophilic component is an additive to the core (forexample, the hydrophilic component may be admixed with a non-hydrophilicpolymer). In further embodiments, the hydrophilic component is presentboth as an additive embedded in the core and as a hydrophilic polymerwhich is part of the core. In some embodiments, the hydrophiliccomponent is an acid-containing monomer or additive, such as a monomeror additive bearing carboxylic acid functional groups.

In some embodiments, one or more of the polymers used to prepare thecore may be converted to a swellable component after the polymer hasalready been prepared. For example, a polymer containing vinyl acetateunits may be hydrolyzed to form a core polymer containing sufficienthydroxy groups such that the polymer is swellable.

The hydrophilic component of the core may be provided by polymerizationor copolymerization of one or more monoethylenically unsaturatedmonomers bearing a hydrophilic functional group such as a carboxylicacid group or some other type of ionizable functional group. In someembodiments, such a monoethylenically unsaturated monomer isco-polymerized with at least one nonionic monoethylenically unsaturatedmonomer.

Examples of hydrophilic monoethylenically unsaturated monomers usefulfor making the core polymer include monoethylenically unsaturatedmonomers containing acid-functionality such as monomers containing atleast one carboxylic acid group or one phosphoric acid group, includingacrylic acid, methacrylic acid, acryloxypropionic acid,(meth)acryloxypropionic acid, itaconic acid, aconitic acid, maleic acidor anhydride, fumaric acid, crotonic acid, monomethyl maleate,monomethyl fumarate, monomethyl itaconate and the like. In certainembodiments, the hydrophilic monoethylenically unsaturated monomer isacrylic acid or methacrylic acid.

Examples of hydrophilic non-polymeric components that may be present inthe core include compounds containing one or more carboxylic acid groupssuch as aliphatic or aromatic monocarboxylic acids and dicarboxylicacids, such as benzoic acid, m-toluic acid, p-chlorobenzoic acid,o-acetoxybenzoic acid, azelaic acid, sebacic acid, octanoic acid,cyclohexanecarboxylic acid, lauric acid and monobutyl phthalate and thelike.

The hydrophilic monoethylenically unsaturated monomer may be present inthe core polymer in amounts of, as polymerized units, from about 5 toabout 80, from about 10 to about 80, from about 20 to about 80, fromabout 30 to about 70, from about 30 to about 60, from about 40 to about60, or from about 30 to about 50, percent by weight, based on the weightof core polymer.

The core polymer may additionally contain recurring units derived fromnon-ionic monomers. Examples of non-ionic monomers that may be presentin polymerized form in the swellable core polymer include vinyl aromaticmonomers such as styrene, a-methyl styrene, p-methyl styrene, t-butylstyrene, or vinyltoluene, olefms such as ethylene, vinyl acetate, vinylchloride, vinylidene chloride, (meth)acrylonitrile, (meth)acrylamide,(C₁-C₂₀) alkyl or (C₃-C₂₀) alkenyl esters of (meth)acrylic acid, such asmethyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate,2-ethyihexyl (meth)acrylate, hydroxyethyl(meth)acrylate,hydroxypropyl(meth)acrylate, benzyl (meth)acrylate, lauryl(meth)acrylate, oleyl (meth)acrylate, palmityl (meth)acrylate, stearyl(meth)acrylate and the like.

The core polymer may further contain polyethylenically unsaturatedmonomer in amounts, as polymerized units, of 0.1 to 20 percent. Examplesof suitable polyethylenically unsaturated monomers include co-monomerscontaining at least two polymerizable vinylidene groups such asα,β-ethylenically unsaturated monocarboxylic acid esters of polyhydricalcohols containing 2-6 ester groups. Such co-monomers include alkyleneglycol diacrylates and dimethacrylates, such as for example, ethyleneglycol diacrylate, ethylene glycol dimethacrylate, 1,3-butylene glycoldiacrylate, 1,4-butylene glycol diacrylate propylene glycol diacrylateand triethylene glycol dimethylacrylate; 1,3-glycerol dimethacrylate;1,1,1-trimethylol propane dimethacrylate; 1,1,1-trimethylol ethanediacrylate; pentaerythritol trimethacrylate; 1,2,6-hexane triacrylate;sorbitol pentamethacrylate; methylene bis-acrylamide, methylenebis-methacrylamide, divinyl benzene, vinyl methacrylate, vinylcrotonate, vinyl acrylate, vinyl acetylene, trivinyl benzene, triallylcyanurate, divinyl acetylene, divinyl ethane, divinyl sulfide, divinylether, divinyl sulfone, diallyl cyanamide, ethylene glycol divinylether, diallyl phthalate, divinyl dimethyl silane, glycerol trivinylether, divinyl adipate; dicyclopentenyl (meth)acrylates;dicyclopentenyloxy (meth)acrylates; unsaturated esters of glycolmonodicyclopentenyl ethers; allyl esters of α,β-unsaturated mono- anddicarboxylic acids having terminal ethylenic unsaturation includingallyl methacrylate, allyl acrylate, diallyl maleate, diallyl fumarate,diallyl itaconate and the like.

The multi-stage emulsion polymer particles may contain one or moreintermediate encapsulating polymer layers. The intermediateencapsulating polymers partially or fully encapsulate the core. Eachencapsulating polymer layer may be partially or fully encapsulated byanother encapsulating polymer layer. Each encapsulating polymer layermay be prepared by conducting an emulsion polymerization in the presenceof the core or a core encapsulated by one or more encapsulatingpolymers. The intermediate encapsulating polymer layer may function as acompatiblizing layer, sometimes referred to as a tie or tie coat layer,between other layers of the multi-stage emulsion polymer particles; forexample, an intermediate encapsulating polymer layer may help adhere theouter shell to the core. An intermediate encapsulating polymer layer mayalso serve to modify certain characteristics of the final voided latexparticles.

At least one intermediate encapsulating polymer may contain, aspolymerized units, one or more hydrophilic monoethylenically unsaturatedmonomers and one or more nonionic monoethylenically unsaturatedmonomers. The hydrophilic monoethylenically unsaturated monomers and thenonionic monoethylenically unsaturated monomers useful for making thecore are also useful for making such an intermediate encapsulatingpolymer. Generally, however, the intermediate encapsulating polymercontains a lower proportion of hydrophilic monomer than the corepolymer, such that the intermediate incapsulating polymer swells lesswhen contacted with the swelling agent. Other intermediate encapsulatingpolymers may contain, as polymerized units, non-ionic monoethylenicallyunsaturated monomer and little or no (e.g., less than 5 weight %)hydrophilic monoethylenically unsaturated monomer. Intermediateencapsulating polymers may further include crosslinking agents such asalkylene glycol diacrylates and dimethacrylates, such as for example,ethylene glycol diacrylate, ethylene glycol dimethacrylate, 1,3-butyleneglycol diacrylate, 1,4-butylene glycol diacrylate propylene glycoldiacrylate and triethylene glycol dimethylacrylate; 1,3-glyceroldimethacrylate; 1,1,1-trimethylol propane dimethacrylate;1,1,1-trimethylol ethane diacrylate; pentaerythritol trimethacrylate;1,2,6-hexane triacrylate; sorbitol pentamethacrylate; methylenebis-acrylamide, methylene bis-methacrylamide, divinyl benzene, vinylmethacrylate, vinyl crotonate, vinyl acrylate, vinyl acetylene, trivinylbenzene, triallyl cyanurate, divinyl acetylene, divinyl ethane, divinylsulfide, divinyl ether, divinyl sulfone, diallyl cyanamide, ethyleneglycol divinyl ether, diallyl phthalate, divinyl dimethyl silane,glycerol trivinyl ether, divinyl adipate; dicyclopentenyl(meth)acrylates; dicyclopentenyloxy (meth)acrylates; unsaturated estersof glycol monodicyclopentenyl ethers; allyl esters of α,β-unsaturatedmono- and dicarboxylic acids having terminal ethylenic unsaturationincluding allyl methacrylate, allyl acrylate, diallyl maleate, diallylfumarate, diallyl itaconate and the like.

The free radical initiators suitable for the polymerization of themonomers used to prepare the multi-stage emulsion polymer particles maybe any water soluble initiator suitable for aqueous emulsionpolymerization. Examples of free radical initiators suitable for thepreparation of the multi-stage emulsion polymer particles of the presentapplication include hydrogen peroxide, tert-butyl peroxide, alkali metalpersulfates such as sodium, potassium and lithium persulfate, ammoniumpersulfate, and mixtures of such initiators with a reducing agent. Theamount of initiator may be, for example, from 0.01 to 3 percent byweight, based on the total amount of monomer.

In some embodiments, a redox polymerization initiator system is used. Ina redox free radical initiation system, a reducing agent may be used inconjunction with an oxidant. Reducing agents suitable for the aqueousemulsion polymerization include sulfites (e.g., alkali metalmetabisulfite, hydrosulfite and hyposulfite). In some embodiments,sugars (such as alkali metal (iso)ascorbate salt, ascorbic acid andisoascorbic acid) might also be a suitable reducing agent for theaqueous emulsion polymerization.

In a redox system, the amount of reducing agent may be, for example,from 0.01 to 3 percent by weight based on the total amount of monomer.

Oxidizing agents include, for example, for example, hydrogen peroxideand ammonium or alkali metal persulfates, perborates, peracetates,peroxides, and percarbonates and a water-insoluble oxidizing agent suchas, for example, benzoyl peroxide, lauryl peroxide, t-butyl peroxide,t-butyl hydroperoxide, 2,2′-azobisisobutyronitrile, t-amylhydroperoxide, t-butyl peroxyneodecanoate, and t-butyl peroxypivalate.The amount of oxidizing agent may be, for example, from 0.01 to 3percent by weight, based on the total amount of monomer.

The free radical polymerization temperature typically is in the range ofabout 10° C. to 100° C. In the case of the persulfate systems, thetemperature may be in the range of about 60° C. to about 100° C. In theredox system, the temperature may be in the range of about 30° C. toabout 100° C., in the range of about 30° C. to about 60° C., or in therange of about 30° C. to about 45° C. The type and amount of initiatormay be the same or different in the various stages of the multi-stagepolymerization.

One or more nonionic or ionic (e.g., cationic, anionic) emulsifiers, orsurfactants, may be used, either alone or together, duringpolymerization in order to emulsify the monomers and/or to keep theresulting polymer particles in dispersed or emulsified form. Examples ofsuitable nonionic emulsifiers includetert-octylphenoxyethylpoly(39)-ethoxyethanol,dodecyloxypoly(10)ethoxyethanol,nonylphenoxyethyl-poly(40)ethoxyethanol, polyethylene glycol 2000monooleate, ethoxylated castor oil, fluorinated alkyl esters andalkoxylates, polyoxyethylene (20) sorbitan monolaurate, sucrosemonococoate, di(2-butyl)phenoxypoly(20)ethoxyethanol,hydroxyethylcellulosepolybutyl acrylate graft copolymer, dimethylsilicone polyalkylene oxide graft copolymer, poly(ethyleneoxide)poly(butyl acrylate) block copolymer, block copolymers ofpropylene oxide and ethylene oxide,2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylated with 30 moles ofethylene oxide, N-polyoxyethylene(20)lauramide,N-lauryl-N-polyoxyethylene(3)amine and poly(10)ethylene glycol dodecylthioether. Examples of suitable ionic emulsifiers include sodium laurylsulfate, sodium dodecylbenzenesulfonate, potassium stearate, sodiumdioctyl sulfosuccinate, sodium dodecyldiphenyloxide disulfonate,nonylphenoxyethylpoly(l)ethoxyethyl sulfate ammonium salt, sodiumstyrene sulfonate, sodium dodecyl allyl sulfosuccinate, palmitic acid,palmitoleic acid, stearic acid, oleic acid, linoleic acid, linolenicacid, mixtures of fatty acids (e.g., linseed oil fatty acid), sodium orammonium salts of phosphate esters of ethoxylated nonylphenol, sodiumoctoxynol-3-sulfonate, sodium cocoyl sarcocinate, sodium1-alkoxy-2-hydroxypropyl sulfonate, sodium α-olefin (C₁₄-C₁₆)sulfonate,sulfates of hydroxyalkanols, tetrasodium N-(1,2-dicarboxyethyl)-N-octadecylsulfosuccinamate, disodiumN-octadecylsulfosuccinamate, disodium alkylamido polyethoxysulfosuccinate, disodium ethoxylated nonylphenol half ester ofsulfosuccinic acid and the sodium salt oftert-octylphenoxyethoxypoly(39)ethoxyethyl sulfate.

The one or more emulsifiers or surfactants are generally used at a levelof from zero to 3 percent based on the weight of the monomers. The oneor more emulsifiers or surfactants can be added prior to the addition ofany monomer charge, during the addition of a monomer charge or acombination thereof.

Suitable swelling agents are generally bases, including volatile basessuch as ammonia, ammonium hydroxide, and volatile lower aliphaticamines, such as morpholine, trimethylamine, and triethylamine, and thelike. Fixed or permanent bases such as sodium hydroxide, potassiumhydroxide, lithium hydroxide, zinc ammonium complex, copper ammoniumcomplex, silver ammonium complex, strontium hydroxide, barium hydroxideand the like may also be used. Solvents, such as, for example, ethanol,hexanol, octanol, and Texanol® solvent and those described in U.S. Pat.No. 4,594,363, may be added to aid in fixed or permanent basepenetration. In some embodiments, the swelling agent is ammonia orammonium hydroxide. The swelling agent may be in the form of an aqueousliquid or a gaseous medium containing a volatile base. The compositionsof the outer shell and any intermediate encapsulating layers may beselected so as to be permeable to the swelling agent at ambienttemperature or at a moderately elevated temperature. In one embodiment,the swelling agent is contacted with the multi-stage emulsion polymerparticles at a temperature somewhat less than the glass transitiontemperature of the outer shell polymer. For example, the contactingtemperature may be 5 to 20° C. less than the outer shell polymer Tg.

The hydrophilic component of the core swells when the multi-stageemulsion polymer particles are subjected to a basic swelling agent thatpermeates the outer shell of the multi-stage emulsion polymer particles(and any intermediate encapsulating layers, if present). In oneembodiment of the invention, the hydrophilic component of the core isacidic (having a pH less than 6). Treatment with a basic swelling agentneutralizes the acidity and raises the pH of the hydrophilic componentgreater than 6, or at least about 7, or to at least about 8, or at leastabout 9, or at least about 10, or to at least about 13, thereby causingswelling by hydration of the hydrophilic component of the core. Theswelling, or expansion, of the core may involve partial merging of theouter periphery of the core into the pores of the inner periphery of thelayer immediately adjacent to the core (such as the outer shell or anintermediate encapsulating shell) and also partial enlargement orbulging of such adjacent layer and the entire particle overall. Swellingmay be carried out before or after the outer shell is formed or beforethe outer shell is completely formed.

The weight ratio of the core to the outer shell may generally, forexample, be in the range of from 1:5 to 1:20 (e.g., from 1:8 to 1:15).To decrease the dry density of the final voided latex particles, theamount of outer shell relative to the amount of core should generally bedecreased; however, sufficient outer shell should be present such thatthe core is still encapsulated.

Methods previously described in the art for producing voided latexparticles may be adapted for use in the present invention, provided thecomposition of the polymer utilized to form the outer shell of suchparticles is modified to provide a functionalized polymer in accordancewith the invention (e.g., an outer shell polymer bearing functionalgroups selected from 1,3-diketo, amino, ureido and urea functionalgroups or combinations thereof, and/or any of the other functionalgroups described herein). Methods for obtaining voided latex particlesare described, for example, in U.S. Pat. Nos. 4,427,836; 4,468,498;4,594,363; 4,880,842; 4,920,160; 4,985,469; 5,216,044; 5,229,209; and5,273,824, each of which is incorporated herein by reference in itsentirety for all purposes. For example, particles in accordance with thepresent invention may be made by incorporating the functional monomersdescribed herein into the outer shell of the particles described in thefollowing examples: (1) examples 0-14 of U.S. Pat. No. 4,427,836, (2)examples 0-12 of U.S. Pat. No. 4,468,498, (3) examples 1-4 of U.S. Pat.No. 4,594,363, (4) examples I-IX of U.S. Pat. No. 4,880,842, (5)examples 1-13 of U.S. Pat. No. 4,920,160, (6) examples 1-7 of U.S. Pat.No. 4,985,469, (7) examples 1-7 of U.S. Pat. No. 5,216,044, (8) examples1-8 of U.S. Pat. No. 5,229,209, and (9) examples 1-50 of U.S. Pat. No.5,273,824.

FIG. 1 illustrates in schematic form an exemplary process which can beused to prepare multi-stage emulsion polymer particles and voided latexparticles in accordance with the invention. In Step 1, methylmethacrylate (MMA) is homopolymerized to form seed 1 as a small particlecomprised of polymethyl methacrylate. Seed 1 is coated with a layer ofmethyl methacrylate/methacrylic acid copolymer by copolymerization ofmethyl methacrylate (MMA) monomer and methacrylic acid (MAA) monomer toprovide core 2 (Step 2). In Step 3, encapsulating polymer layer 3 isformed by copolymerization of styrene (S) monomer and methylmethacrylate (MMA) monomer. In this embodiment, encapsulating polymerlayer 3 is capable of functioning as a tie-coat between core 2 and outershell 4, which is formed in Step 4 by copolymerization of styrene (S)monomer and a functionalized monomer (FM) such as an imidazolidinone(meth)acrylic monomer. In other embodiments, encapsulating polymer layer3 may be omitted. More than one encapsulating polymer layer between corelayer 2 and outer shell 4 may be present, if so desired. A multi-stageemulsion polymer particle 7 is obtained following Step 4. Multi-stageemulsion polymer particle 7 is contacted with aqueous ammonium hydroxidein Step 5. The ammonium hydroxide acts as a swelling agent, wherein thecarboxylic acid functional groups of the MMA/MAA copolymer of core 2 areat least partially neutralized and core 2 swells in volume as a resultof absorption of water by neutralized core 2. The volume increase ofcore 2 pushes encapsulating polymer layer 3 and outer shell 4 outwardlyand the overall diameter of the multi-stage emulsion polymer particleincreases. Drying the particles in Step 6 provides voided latex particle6. Voided latex particle 6 is characterized by having an outer shell 4surrounding hollow interior 5, wherein the outer shell 4 is comprised ofa polymer bearing functional groups such as ureido functional groupsderived from the functionalized monomer. Residues of seed 1 and core 2may still be present within hollow interior 5.

The voided latex particles in accordance with the present invention areuseful in coating compositions, such as aqueous-based paint and papercoatings. Voided latex particles in accordance with this invention maybe capable of imparting improved gloss, brightness and opacity to papercoating formulations to which they are added. Also, voided latexparticles in accordance with this invention may be capable of impartingopacity to aqueous coating compositions, such as paints, to which theyare added. In addition, the wet adhesion of coating compositions can beimproved by including voided latex particles in accordance with thisinvention, especially where the outer shell polymer contains functionalgroups selected from 1,3-diketo, amino, ureido and urea functionalgroups.

For example, a coating composition may contain, in addition to water,voided latex particles in accordance with this invention, one or morefilm-forming latex polymers (e.g., an acrylic (A/A) latex and/or a vinylacrylic (V/A) latex), and, if so desired, any of the additives or othercomponents typically employed in such latex coating compositions such ascoalescing solvents, biocides, pigments, fillers, opacifying agentsother than the voided latex particles (e.g., titanium dioxide, CaCO₃),thickeners, leveling agents, pH adjusting agents, surfactants,antifreeze agents and the like. Voided latex particles may be present insuch coating compositions at levels of, for example, 0.5 to 10 weightpercent.

The film-forming latex polymer used in combination with the voided latexparticles of the present invention may also be selected such that italso contains functional groups which help to modify or enhance certaincharacteristics of the coating composition, such as wet adhesion, scrubresistance, solvent resistance, stain resistance or the like. Forexample, the film-forming latex polymer may be a polymer prepared bypolymerization of a so-called wet adhesion monomer, optionally incombination with one or more other types of comonomers. The wet adhesionmonomer may be, for instance, an ethylenically unsaturated compoundbearing a urea, ureido, 1,3-diketo, amino or other such functionalgroup. Such functionalized film-forming latex polymers are well known inthe art and are described, for example, in U.S. Pat. Nos. 3,935,151;3,719,646; 4,302,375; 4,340,743; 4,319,032; 4,429,095; 4,632,957;4,783,539; 4,880,931; 4,882,873; 5,399,706; 5,496,907; and 6,166,220,each of which is incorporated herein by reference in its entirety forall purposes.

In one embodiment of the invention, a film-forming latex polymer isselected for use in a coating composition in combination with thenon-film-forming voided latex particles described herein wherein thefilm-forming latex polymer contains functional groups capable ofinteracting with the functional groups present in the outer shell of thenon-film-forming voided latex particles so as to provide a crosslinkingeffect. Such crosslinking effect may result when the coating compositionis applied to a substrate surface and dried, for example. Thisinteraction typically takes place through chemical reaction between thetwo types of functional groups resulting in the formation of covalentbonds, although the interaction could alternatively be the result of anon-covalent association such as complexation or formation of a salt.The opacity and solvent resistance of the coating may, for example, beenhanced through the use of such functionalized film-forming latexpolymer and functionalized non-film-forming voided latex particles incombination with each other.

Examples of pairs of functional groups capable of interacting with eachother are as follows. Functional Group A may be on the non-film-formingvoided latex particles (as part of the outer shell polymer) andFunctional Group B may be present in the film-forming latex polymercomponent. Alternatively, Functional Group A may be present in thefilm-forming polymer and Functional Group B may be present in the outershell of the non-film-forming voided latex particles.

Functional Group Pair Functional Group A Functional Group B 1 CarbonylHydrazide 2 Epoxy Amine 3 Oxazoline Aldehyde 4 AAEM (acetoacetyl Amineethyl methacrylate

In yet another embodiment of the invention, the coating composition isformulated so as to contain one or more non-polymeric compounds bearingtwo or more functional groups per molecule capable of interacting withthe functional groups present in the outer shell of the non-film-formingvoided latex particles. Such non-polymeric compounds thus also mayfunction as crosslinking agents. For example, where the outer shellcontains acetoacetate groups, a non-polymeric compound containing aplurality of primary amine groups on each molecule may be employed.

In still another embodiment, the functional groups present in the outershell of the non-film-forming voided latex particles are selected so asto be capable of condensing with each other thereby forming linkagesbetween different particles. For instance, the outer shell may bear—Si(OH)₃ functional groups which may undergo a dehydration reaction toform a siloxane linkage (e.g., —Si(OH)₂—O—Si(OH)₂—).

EXAMPLES

The binders (film forming latexes) used were commercial samples. The A/Alatex (ENCOR (previously known as UCAR) Latex 634, supplied by ArkemaInc.) and the V/A latex (ENCOR (previoiusly known as UCAR) Latex 300,also supplied by Arkema Inc.) have identical glass transitiontemperatures (T_(g)) of 4° C. and can be formulated to form a film atroom temperature without the need for coalescing solvents.

The opacifiers were evaluated in the paint formulations outlined inTables 3 and 4. The paints were all formulated at 35% pigment volumeconcentration (PVC) and 40.0% volume solids. All the paints were tintedwith 1.25 ozs/gallon of Colortrend® 888, Colorant B (lamp black).

The paints outlined in Table 1 contained 50 to 200 lbs/100 gallons TiO₂with the remaining “pigment” volume being made up with opacifier, whichresulted in opacifier use levels ranging from 40 to 60 dry lbs/100gallons. This is above current standard opacifier usage, which typicallyvaries from 10 to 30 dry lbs/100 gallons. V/A-A/A blend ratios of 100-0,92.5-7.5, and 85-15% were explored. In Tables 1 and 2, opacifier SampleA is the Control, wherein the outer shell of the voided latex particlesis a styrene homopolymer. The other opacifiers tested, Sample B andSample C, were voided latex particles in accordance with the inventioncontaining outer shells comprised ofstyrene/2-(2-oxo-1-imidazolidinyl)ethyl methacrylate copolymercontaining 2 phm and 4 phm of polymerized2-(2-oxo-1-imidazolidinyl)ethyl methacrylate (hereafter referred to as“functionalized monomer” or “FM”) respectively.

TABLE 1 Ingredient Form 1 Form 2 Form 3 Form 4 Form 5 Form 6 Form 7 Form8 Form 9 Ti-Pure R-746 65.4 65.4 65.4 261.4 261.4 261.4 163.4 163.4163.4 Water 180.7 180.7 180.7 167.5 167.5 167.5 171.4 171.4 171.4 NH4OH,28% 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Sample A Opacifier 201.4 0.0 0.0128.8 0.0 0.0 165.1 0.0 0.0 Sample B 0.0 201.4 0.0 0.0 128.8 0.0 0.0165.1 0.0 Sample C 0.0 0.0 201.4 0.0 0.0 128.8 0.0 0.0 165.1 UCAR 300448.3 448.3 448.3 448.2 448.2 448.2 413.7 413.7 413.7 UCAR 634 0.0 0.00.0 0.0 0.0 0.0 36.8 36.8 36.8 Water Slurried 0.0 0.0 0.0 0.0 0.0 0.00.0 0.0 0.0 Tamol 1124 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Omyacarb UF0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Polyphobe TR-115 6.3 6.3 6.3 6.3 6.36.3 5.9 5.9 5.9 Polyphobe TR-117 6.3 6.3 6.3 6.3 6.3 6.3 6.6 6.6 6.6Total 909.7 909.7 909.7 1019.9 1019.9 1019.9 964.4 964.4 964.4 PVC 35.035.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 wt % 39.7 39.7 39.7 48.0 48.048.0 43.8 43.8 43.8 vol % 40.0 40.0 40.0 40.0 40.0 40.0 40.0 40.0 40.0Density, lbs/gallon 9.10 9.10 9.10 10.25 10.25 10.25 9.67 9.67 9.67Volume, gallons 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0Ingredient Form 10 Form 11 Form 12 Form 13 Form 14 Form 15 Ti-Pure R-74665.4 65.4 65.4 261.4 261.4 261.4 Water 175.3 175.3 175.3 162.1 162.1162.1 NH4OH, 28% 1.5 1.5 1.5 1.5 1.5 1.5 Sample A Opacifier 201.4 0.00.0 128.8 0.0 0.0 Sample B 0.0 201.4 0.0 0.0 128.8 0.0 Sample C 0.0 0.0201.4 0.0 0.0 128.8 UCAR 300 379.3 379.3 379.3 379.1 379.1 379.1 UCAR634 73.6 73.6 73.6 73.6 73.6 73.6 Water Slurried 0.0 0.0 0.0 0.0 0.0 0.0Tamol 1124 0.0 0.0 0.0 0.0 0.0 0.0 Omyacarb UF 0.0 0.0 0.0 0.0 0.0 0.0Polyphobe TR-115 5.6 5.6 5.6 5.5 5.5 5.5 Polyphobe TR-117 6.9 6.9 6.97.0 7.0 7.0 Total 909.0 909.0 909.0 1019.0 1019.0 1019.0 PVC 35.0 35.035.0 35.0 35.0 35.0 wt % 39.6 39.6 39.6 47.9 47.9 47.9 vol % 40.0 40.040.0 40.0 40.0 40.0 Density, lbs/gallon 9.09 9.09 9.09 10.24 10.24 10.24Volume, gallons 100.0 100.0 100.0 100.0 100.0 100.0

Additional paints were prepared to explore coating performance at loweropacifier loadings. The paints outlined in Table 2 were also preparedwith 50 to 200 lbs/100 gallons TiO₂ with the remaining “pigment” volumebeing made up with either opacifier or CaCO₃, which resulted inopacifier use levels ranging from 0 to 60 dry lbs/100 gallons.

TABLE 2 Ingredient Form 1 Form 2 Form 3 Form 4 Form 5 Form 6 Form 7 Form8 Form 9 Form 10 Form 11 Ti-Pure R-746 65.4 261.4 65.4 261.4 163.4 163.465.4 163.4 163.4 261.4 163.4 Water 135.0 138.5 180.7 167.5 155.4 136.8157.9 151.2 159.6 153.0 174.1 NH4OH, 28% 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.51.5 1.5 1.5 Sample A Opacifier 0.0 0.0 201.4 128.8 82.5 0.0 100.7 64.4100.7 64.4 165.1 Sample B 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0Sample C 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 UCAR 300 448.0448.0 448.3 448.2 448.1 448.0 448.2 448.1 448.2 448.1 448.3 UCAR 634 0.00.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Water Slurried 111.6 71.2 0.00.0 45.7 91.4 55.8 55.8 35.6 35.6 0.0 Tamol 1124 27.9 17.8 0.0 0.0 11.422.9 14.0 14.0 8.9 8.9 0.0 Omyacarb UF 279.0 178.0 0.0 0.0 114.3 228.5139.5 139.5 89.0 89.0 0.0 Polyphobe TR-115 6.3 6.3 6.3 6.3 6.3 6.3 6.36.3 6.3 6.3 6.3 Polyphobe TR-117 6.3 6.3 6.3 6.3 6.3 6.3 6.3 6.3 6.3 6.36.3 Total 1080.9 1128.9 909.7 1019.9 1034.8 1104.9 995.3 1050.4 1019.31074.4 964.8 PVC 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0wt % 53.7 55.8 39.7 48.0 49.3 54.8 46.7 50.9 47.8 51.9 43.9 vol % 40.040.0 40.0 40.0 40.0 40.0 40.0 40.0 40.0 40.0 40.0 Density, lbs/gallon10.8 11.3 9.10 10.25 10.4 11.1 10.0 10.5 10.2 10.8 9.7 Volume, gallons100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

Wet adhesion refers to the ability of a latex paint to adhere to asubstrate under wet conditions. Poor wet adhesion can lead toblistering, peeling, flaking and chipping when the coating is exposed toperiods of precipitation and/or temperature-humidity cycles.

The wet adhesion test used herein measures the adhesion of a coatingunder wet conditions to an aged alkyd substrate. The gloss alkyd panelswere prepared by casting a 7-mil film of Glidden Glid-Guard® 4554 glossalkyd paint onto a Leneta scrub chart and allowing it to cure for 3 to 6weeks at 25° C. and 50% relative humidity. The test and control paintswere drawn down in parallel on the same alkyd panel with a 7-mil Dowbar. After the panels were dried for 24 hours at 25° C. and 50% relativehumidity, the films were crosshatched through to the gloss alkydsubstrate layer. The test panels were then soaked in water for 30minutes. Size and density of blisters were noted. Before scrubbing, 20mL of 50% Lava® soap solution and 5 mL of water were added to the paintpanels on the scrub machine. The reported results include the number ofcycles at which initial failures were observed and the percent filmremaining after 500 cycles.

FIG. 2 illustrates the impact of A/A latex modification, voided latexparticle opacifier level, and functionalized monomer content of theouter shells of the voided latex particles on wet adhesion to a glossalkyd substrate. The paints modified with 7.5% A/A latex and voidedlatex particles in accordance with the invention (where the outer shellcomprised a functionalized polystyrene, where in functionalized monomercontent was 2 or 4 phm) had some degree of failure but likely representthe minimum level required for acceptable performance. By contrast,paints modified with 15% A/A latex and a conventional voided latexparticle opacifier (containing a styrene homopolymer outer shell) didnot achieve adequate wet adhesion performance.

1. A voided latex particle comprising a hollow interior and an outershell, wherein the outer shell is comprised of an outer shell polymerhaving a Tg of at least above 45° C. and bearing functional groupsselected from 1,3-diketo, amino, ureido, urea, hydroxyl, polyether,silane, phosphate, epoxy, fluorocarbon, aldehyde, ketone, acetoacetyl,functional groups or combinations thereof and wherein the voided latexparticle is non-film-forming and opaque.
 2. The voided latex particle ofclaim 1, wherein the outer shell polymer is a copolymer of a vinylaromatic polymer and a free radical polymerizable ethylenicallyunsaturated monomer containing a ureido or urea functional group.
 3. Thevoided latex particle of claim 2, wherein the vinyl aromatic monomerstyrene.
 4. The voided latex particle of claim 2, wherein the freeradical polymerizable ethylenically unsaturated monomer contains a(meth)acrylate or (meth)acrylamide group.
 5. The voided latex particleof claim 2, wherein the free radical polymerizable ethylenicallyunsaturated monomer is an imidazolidinone (meth)acrylic monomer.
 6. Thevoided latex particle of claim 2, wherein the free radical polymerizableethylenically unsaturated monomer is selected from the group consistingof 2-(2-oxo- 1-imidazolidinyl)ethyl (meth)acrylates andN-(2-(2-oxo-1-imidazolidinyl)ethyl (meth)acrylamides.
 7. The voidedlatex particle of claim 2, wherein the copolymer contains from 0.1 to 10weight % of the free radical polymerizable ethylenically unsaturatedmonomer.
 8. The voided latex particle of claim 1, wherein the functionalgroups are introduced to the outer shell polymer by polymerization ofone or monomers bearing the functional groups.
 9. The voided latexparticle of claim 1, wherein the functional groups are introduced to theouter shell polymer by reacting a precursor polymer with afunctionalization agent capable of forming the functional groups. 10.The voided latex particle of claim 2, wherein the free radicalpolymerizable ethylenically unsaturated monomer is selected from thegroup consisting of acetoacetoxy(meth)acrylates, allyl acetoacetate,methylolated diacetone (meth)acrylamides, aminoalkyl(meth)acrylates, andethylenically unsaturated polymerizable aziridinyl monomers.
 11. Thevoided latex particle of claim 1, wherein the voided latex particlefurther comprises at least one intermediate encapsulating polymerbetween the hollow interior and the outer shell.
 12. The voided latexparticle of claim 11, wherein the intermediate encapsulating polymercomprises at least one non-ionic monoethylenically unsaturated monomerand at least one crosslinking agent.
 13. The voided latex particle ofclaim 1, wherein the outer shell polymer has a glass transitiontemperature of at least 60° C.
 14. The voided latex particle of claim 1,wherein the outer shell polymer contains 0.05 to 5 weight % of thefunctional groups.
 15. A process for forming voided latex particleswhich are non-film-forming, wherein the process comprises contactingmulti-stage emulsion polymer particles comprising a core and an outershell with a swelling agent, wherein: the core comprises a hydrophiliccomponent; the outer shell comprises an outer shell polymer having a Tgof at least 45° C. and bearing functional groups selected from1,3-diketo, amino, ureido, urea, fluorocarbon, phosphate, epoxy,hydroxyl, silane, aldehyde, ketone, acetoacetyl, or combinationsthereof; and the swelling agent is capable of swelling the core.
 16. Theprocess of claim 15, wherein the multi-stage emulsion polymer particlesfurther comprise at least one intermediate encapsulating polymercomprised of at least one non-ionic monoethylenically unsaturatedmonomer and at least one hydrophilic monoethylenically unsaturatedmonomer.
 17. The process of claim 15, wherein the outer shell polymer isa copolymer comprised of a vinyl aromatic polymer and a free radicalpolymerizable ethylenically unsaturated monomer containing a ureido orurea functional group.
 18. The process of claim 17, wherein the freeradical polymerizable ethylenically unsaturated monomer contains a(meth)acrylate or (meth)acrylamide group.
 19. The process of claim 17,wherein the free radical polymerizable ethylenically unsaturated monomeris an imidazolidinone (meth)acrylic monomer.
 20. The process of claim17, wherein the free radical polymerizable ethylenically unsaturatedmonomer is selected from the group consisting of2-(2-oxo-1-imidazolidinyl)ethyl (meth)acrylates andN-(2-(2-oxo-1-imidazolidinyl)ethyl (meth)acrylamides.
 21. The process ofclaim 17, wherein the copolymer is comprised of from 0.1 to 10 weight %of the free radical polymerizable ethylenically unsaturated monomer. 22.The process of claim 15, wherein the functional groups are introduced tothe outer shell polymer by polymerization of one or monomers bearing thefunctional groups.
 23. The process of claim 15, wherein the functionalgroups are introduced to the outer shell polymer by reacting a precursorpolymer with a functionalization agent capable of forming the functionalgroups.
 24. The process of claim 15, wherein the free radicalpolymerizable ethylenically unsaturated monomer is selected from thegroup consisting of acetoacetoxy(meth)acrylates, allyl acetoacetate,methylolated diacetone (meth)acrylamides, aminoalkyl(meth)acrylates, andethylenically unsaturated polymerizable aziridinyl monomers.
 25. Acoating composition comprising the voided latex particles in accordancewith claim
 1. 26. The coating composition of claim 25, furthercomprising film-forming latex particles.
 27. The coating composition ofclaim 26, wherein at least a portion of the film-forming latex particlesbear functional groups capable of interacting with the functional groupspresent in the outer shell polymer.
 28. The coating composition of claim25, further comprising at least one non-polymeric compound bearing twoor more functional groups per molecule capable of interacting withfunctional groups present in the outer shell polymer.
 29. A coatingcomposition comprising the voided latex particles in accordance withclaim
 1. 30. The coating composition of claim 29, further comprisingfilm forming latex particles.
 31. The coating composition of claim 30,wherein at least a portion of the film-forming latex particles bearfunctional groups capable of interacting with the functional groupspresent in the outer shell.
 32. The coating composition of claim 29,further comprising at least one non-polymeric compound bearing two ormore functional groups per molecule capable of interacting withfunctional groups present in the outer shell polymer.
 33. The coatingcomposition of claim 30, wherein said latex is an acrylic or vinylacrylic latex.
 34. A paint comprising the coating composition of claim30.
 35. The paint composition of claim 34, wherein said latex is anacrylic, styrene acrylic or vinyl acrylic latex.
 36. The paintcomposition of claim 34, further comprising one or more of coalescingsolvents, biocides, pigments, fillers, titanium dioxide, calciumcarbonate, thickeners, leveling agents, pH adjusting agents,surfactants, or antifreeze agents.
 37. The paint composition of claim36, wherein said voided latex particles comprise 0.5 to 10 weightpercent of the paint.
 38. (canceled)
 39. (canceled)
 40. (canceled) 41.The coating composition of claim 33, wherein vinyl/acrylic toacrylic/acrylic blend ratio is between 92.5-7.5, and 85-15%